1. Technical Field
The present invention relates to a parallel link mechanism and an industrial robot.
2. Related Art
General requirements for industrial robots include increased operation speed, improved operation accuracy, and, in certain operation sites, enhanced cleanliness. There are demands that the industrial robots be used under particular circumstance involving use of specific gases or chemicals. One known vertical movement shaft mechanism of a SCARA robot includes a ball screw provided in a vertical movement shaft. The mechanism has a contractible and extensible bellows as a protecting member for preventing release of dust and leakage of grease from the interior of an arm to the external environment.
However, when the bellows extends and contracts, the pressure in the vertical movement shaft mechanism changes, inducing the dust release and the grease leakage. It is thus difficult for the vertical movement shaft mechanism having the bellows to maintain the increased cleanliness. Further, to sufficiently prolong mechanical life of the bellows of the vertical movement shaft mechanism, the bellows must be formed of material selected from a limited range. This makes it difficult to operate the vertical shaft mechanism having the bellows under the aforementioned particular circumstances.
To solve the problem, a vertical movement shaft mechanism of an industrial robot including a parallel link mechanism, but not a bellows, has been proposed. Specifically, as described in Japanese Laid-Open Patent Publication No. 2002-326181, the mechanism includes a first arm connected to a fixed base and a connection base and a second arm connected to the connection base and a movable base. A drive motor is provided in the fixed base and a plurality of spur gears are arranged in the connection base. The drive motor drives the spur gears through a reducer, causing the spur gears to transmit rotational force to the two arms. This vertically moves the movable base.
The vertical movement shaft mechanism of Japanese Laid-Open Patent Publication No. 2002-326181 operates without using a bellows, or is a bellows-less type. Instead, the mechanism includes a transmission mechanism employing the spur gears for rotating the two arms. It is thus necessary to engage the teeth of the spur gears together when assembling the industrial robot, which makes such assembly complicated.